This invention relates generally to a friction roll conveyor clutch apparatus for adjusting the amount of torque transmitted to transportation rollers in a friction roll line shaft conveyor.
In automated material handling, conveyors are used to transmit driving force to media that must be transported from one location to another. This driving force is applied in a manner that advances the media in a desired material flow direction. One type of conveyor commonly used in material handling is a friction roll conveyor. Friction roll conveyors are distinguishable from other conveyors because they do not include endless conveyor xe2x80x9cbeltsxe2x80x9d. Instead, such conveyors transmit driving force from a conveyor motor to transported media by driving a series of transportation rollers that support the media directly. In friction roll conveyors the motor is generally connected to and rotates a line shaft. A plurality of roller shafts are connected to and driven by the line shaft through bevel gears. Two or more transportation rollers are generally fixed in spaced locations along each roller shaft.
Because of part accumulations, jams and other blockages can occur on such conveyors, it is desirable to incorporate means for limiting the amount of torque transmitted to the transportation rollers of such conveyors. By limiting the amount of torque that a drive motor can transmit to the transportation rollers, the rollers are allowed to stop rotating completely when the articles supported on them are jammed or blocked and forced to stop moving or slow significantly. This can prevent damage to the rollers and other conveyor drive components as well as the articles being transported on the conveyor and permit a plurality of articles to accumulate on the conveyor.
In some friction roll conveyors that include transportation rollers mounted on and rotated by rotating roller shafts, the shafts are designed to slip in relation to the rollers. This allows the rollers to stop or slow should an article supported on them be jammed or blocked. The maximum amount of torque that can be transmitted from a roller shaft to a transportation roller before the shaft begins slipping within the roller is limited by the amount of friction between the roller and shaft. The amount of friction between roller and shaft is related to the weight of the media supported by the roller, the clearance between the roller and shaft as well as the shaft and roller material. The friction between rollers and roller shafts in such conveyors is not operator-adjustable and unplanned and unwanted slippage can occur even when conveyed articles are not jammed or blocked in any way. Unwanted slippage can result from variations in the weight of transported articles that changes the frictional force or torque between supporting roller shafts and transportation rollers. In addition, the intrusion of substances such as metal cutting lubricants between the transportation rollers and their supporting shafts can unpredictably reduce frictional force and driving force transmission. Such factors make it difficult to accurately predict and control the speed at which a conveyor will transport media as well as when a part will stall on the conveyor.
More recent friction roll conveyor designs include provisions for adjusting the amount of torque transmitted to transportation rollers and provide greater control and predictability. For example, as shown in FIG. 1 of the drawings, the prior art includes a line shaft conveyor clutch 10 that includes a compression spring 12 coaxially disposed around a line shaft 14 between a driver bevel gear 16 and a clamp collar 18. The driver bevel gear 16 is fixed against axial movement away from the spring 12 by a second clamp collar 20 that is fixed to the line shaft 14 axially opposite the spring 12 but may be moved to adjust spring compression. The conveyor clutch 10 of FIG. 1 also includes a first driven thrust washer 22 supported on the line shaft 14 between the driver bevel gear 16 and the second clamp collar 20 and a second driven thrust washer 23 supported on the line shaft 14 between the driver bevel gear 16 and the first clamp collar 18. Prior art clutches having designs similar to that shown in FIG. 1 are hard to adjust, and are complex and expensive both to make and to assemble on a conveyor. To adjust spring compression, an operator must estimate the amount of compression change required, manually compress or decompress the spring 12, then loosen, reposition and tighten the clamp collar 18 while attempting to hold the spring 12 at the estimated degree of compression. Clutches of the type shown at 10 in FIG. 1 cannot be assembled separately and stocked as inventory because their various parts can only be assembled together if the clamp collars 18, 20 are fixed to a line shaft 14. Because it cannot be preassembled, the time required for assembling a conveyor that includes such clutches is greater than it would otherwise be. This is because conveyor assembly must include the steps of assembling the clutch 10 by sliding each separate component 20, 22, 16, 12 and 18, in order, onto the line shaft 14 and properly positioning each component before tightening the clamp collars 20, 18. Clutch maintenance and repair is also time-consuming because each component must be disassembled and removed from the line shaft 14, then returned to the line shaft 14 in order and properly positioned before being secured. Moreover, unless the clutch to be repaired is located at the end of the line shaft 14, other clutches supported at spaced-apart locations along the line shaft must also be disassembled before they can be removed to allow access to the damaged clutch. The components of all the removed clutches must then be individually replaced, in order, and properly repositioned on the line shaft when repairs are complete.
Another friction roll conveyor clutch design that provides an adjustment for the amount of torque transmitted to transportation rollers is disclosed in Japanese Patent 61-254405 issued in 1986. Each clutch disclosed in this Japanese patent includes a compression spring that is coaxially disposed around a line shaft between a driver bevel gear and a jam nut. The driver bevel gear is fixed against axial movement away from the spring by a collar that is fixed to the line shaft axially opposite the spring. The friction roll conveyor clutch apparatus disclosed in the Japanese patent also includes a driven thrust washer that is supported on the line shaft between the driver bevel gear and the spring. The jam nut is coaxially and threadedly engaged on the line shaft so that spring compression can be adjusted by axially advancing or retracting the jam nut along the line shaft. However, a friction roll conveyor clutch apparatus constructed according to the Japanese patent cannot be assembled and stocked as inventory, be quickly installed by pre-assembling before mounting on a line shaft, and cannot be quickly removed from a line shaft as a single unit for maintenance or repair.
A clutch apparatus is provided that adjusts the amount of torque transmitted to a transportation roller in a friction roll line shaft conveyor. The conveyor includes a line shaft rotatably driven by a conveyor motor and each transportation roller is fixed on a roller shaft that is rotatably driven by the line shaft. The clutch apparatus includes a driver bevel gear configured to be rotatably mounted around the conveyor line shaft and to drivingly engage a driven bevel gear fixed to the roller shaft to couple drive power from the line shaft to the roller shaft. A compression spring is coaxially disposed between the driver bevel gear and a first stop collar. A second stop collar is coaxially disposed adjacent the driver bevel gear axially opposite the spring.
What characterizes the invention is that the clutch includes an annular hub that is coaxially supportable on and rigidly connectable to the conveyor line shaft and coaxially supports the driver bevel gear, the spring and the stop collars. Therefore, the clutches of a friction roll conveyor apparatus constructed according to the invention may be assembled and stocked as inventory, quickly installed by pre-assembling before mounting on the line shaft, and quickly removed from the line shaft as a single unit for maintenance or repair. A clutch constructed in this manner may also be readily retrofit on the line shafts of existing conveyors.
According to another aspect of the invention, the clutch includes an adjustable stop collar in the form of a jam nut. The use of a jam nut instead of a more permanent stop such as a clamp collar allows an operator to adjust spring compression more accurately and quickly by simply rotating the jam nut. A second jam nut may be incorporated to provide further security against xe2x80x9cunwindingxe2x80x9d and a resulting inadvertent decrease in spring tension.
The invention also includes a method for assembling a friction roll conveyor. The method includes pre-assembling the clutch, providing a driven bevel gear on one end of a roller shaft and providing the clutch on the line shaft such that the driving bevel gear of the clutch operatively engages the driven bevel gear.
Objects, features and advantages of this invention are to provide a friction roll conveyor having clutches that can be easily reconfigured to accommodate conveyed media of different weights and surface textures, that can compensate for the presence of substances that affect the ability of transportation rollers to move the media at constant and predictable speeds, that allow an operator to compensate for such factors by adjusting the axial position of a jam nut or jam nuts of each clutch, that can be pre-assembled and therefore may be stocked as inventory and installed quickly in a conveyer, that minimize clutch wear by allowing easy and accurate adjustment, that include relatively simple components that are inexpensive to make, and that are readily retro fit into existing line shaft conveyer designs.